Traditional cellular systems break down a geographic area into groupings of cells. Each cell provides communication services to mobile stations contained within that cell. In order to provide these services, a base station provides a broadcast control channel upon a predetermined frequency from which all mobile stations contained within the cell can listen. In response, a mobile station can transmit a random access channel burst back to the serving base site where upon the base site allocates a traffic channel for which the mobile station may communicate to the base site for providing communication services such as voice and or data services.
There is an inherent limitation on the number of mobile stations to which a base site may provide communication services. This limitation is determined by the cell size, the frequency reuse pattern of the cell and its surrounding cells and the number of frequencies or traffic channels allocated to the cellular system. In order to increase the capacity provided by a cellular system the physical size of the cells may be reduced, thus, providing more cells within a particular system.
As cellular systems become more prevalent in our society and the usage of the systems increases, there is a need to provide more capacity within the cellular systems. When implementing cellular systems within large buildings there are many sources of interference and also a large concentration of people that could use the system. Traditional systems provide many extremely small cells to provide service to all the users within the building. By providing this plurality of very small cells, there is often a need to hand over more frequently between the cells creating a large amount of overhead communications between cells. Examples of such handover procedures may be found in the Global System for Mobile communications (GSM) recommendations.
Additionally, these systems are extremely sensitive to interference caused by adjacent cells, consequently they are fixed geographically and must be re-planned for each change in the dynamics of the system.
FIG. 1 is an illustration of a cellular communication system 100 that provides communication service in three distinct cellular cells 101, 103 and 105. Each of the three cell sites include a base station 107, 109 and 111 that transmit a broadcast control channel for that particular geographic area defined by the cell. Additionally, each mobile station 113, 115 and 117 contained within the respective cells transmit Random Access Channel (RACH) bursts back to the base site 107, 109 and 111. If the physical size of these cells shrink to a few meters in diameter, the complexity in handing off between a first cell 101 and a second cell 103 become more frequent and more cumbersome in the system architecture. Additionally, cell overlap creates interference problems which are immeasurable by the conventional system and therefore discouraged. Thus in order to properly design such a small system the placement of the cells must be carefully planned and any changes such as office re configuration tearing down walls or just moving furniture within the offices can create enough overlap for which a cellular re plan is required creating a large amount of headache for system implementers.
Thus, it would be advantageous to provide a cellular system that could service a high concentration of users in a small geographic area, such as users in a large office building, without the cumbersome handover procedures and frequency planning procedures that are currently necessary.